Reduce Risk Taking

Many studies done have shown increased risk taking behavior in individuals after low frequency transcranial magnetic stimulation, which transiently suppresses the cortical excitability over the right dorsolateral prefrontal cortex (DLPFC). It appeared likely that Increasing the right DLPFC while simultaneously decreasing the left would have the opposite effect and actually decrease the risk taking behavior in the particular individuals. Thirty six healthy volunteers performed the risk task while they were given either anodal over the right/cathodal on the left, anodal on the left/cathodal on right or sham stimulation.

All of the volunteers did not experience any adverse effects during or after the tDCS. The volunteers reported a slight itching sensation under the electrodes for the first 30 seconds of stimulation even the volunteers on the sham stimulation reported the same effects.

Results revealed a main effect of group ( p 0.0001): participants with right anodal/left cathodal stimulation chose more often low-risk prospects compared with participants with sham stimulation [odds ratio (OR), 2.5; 95% confidence interval (CI), 1.8 –3.3] and those with left anodal/right cathodal (OR, 2.8; 95% CI, 2.1–3.8). Moreover, there was no difference between groups receiving left anodal/right cathodal and sham stimulation (OR, 0.88; 95% CI, 0.7–1.1) (Fig. 2). Also, there was no significant difference between women and men in their choices (unpaired t test, p 0.46). We then tested whether the balance of reward influenced the choice of the low-risk prospect, as reported previously (Rogers et al., 1999; Knoch et al., 2006a). Results revealed a significant main effect of balance of reward ( p0.0019): participants tended to choose less often the low-risk prospect, compared with the risky one, when its associated rewardwas diminished. We theninvestigatedwhether the difference in regard to the balance of reward was similar across groups andfound a significant interaction between groupbalance of reward ( p 0.0001). Participants with right anodal/left cathodal choose more often the safe prospect, regardless of its associated reward, compared with participants with sham stimulation [reward 90:10, p 0.01; reward 80:20, p 0.01; reward 70:30, p 0.001; reward 60:40, p 0.01; significance threshold for the Bonferroni correction (corrected p value) was 0.0125]. Participants with right anodal/left cathodal appeared to be so conservative in their choice that that they were not even influenced by the reward. Finally, there was a significant interaction effect of group level of risk balance of reward ( p 0.0001), suggesting that tDCS was also an effect modifier for the level of risk (4:2, 5:1). In regard to the total points earned, participants receiving right anodal/left cathodal earned significantly more points compared with those receiving left anodal/right cathodal [p 0.0468; significance threshold for the Bonferroni correction (corrected p value) was 0.025], but not compared with sham stimulation ( p 0.1121). There was no difference between the total points earned between participants with left anodal/right cathodal compared with sham stimulation ( p 0.4257) (Fig. 3). We also tested whether the decision times were longer when participants were confronted to a 4:2 versus a 5:1 scenario, as found by Rogers et al. (1999) and Knoch et al. (2006a). There was a main effect of level of risk (F 11.87; p 0.001). Participants decided slower when confronted with the safer scenario (4:2 choice) compared with the higher-risk scenario (5:1 choice). There was no interaction group level of risk ( p 0.18). However, there was a significant difference across the groups. Compared with sham stimulation, participants with right anodal/left cathodal stimulation were significantly faster ( p 0.0001) and those with left anodal/right cathodal stimulation were significantly slower ( p 0.0029). Furthermore, there was a significant interaction across group balance of reward [p 0.0001; significance threshold for the Bonferroni correction (corrected p value) was 0.0125], suggesting that differences in decision time between groups varied according to the reward. We also found a significant interaction between group level of risk balance of reward ( p 0.0001). Finally, there was no significant gender difference in terms of decision time (ANOVA, p 0.689).